That's 20 different kinds of ships! And that's assuming the Shelley, Centaur, Yeager, etc. we see were simply forced into service and decommissioned after the war and don't really count. Or that the apocryphal Constitution, Constellation sightings in the DS9 run weren't actually there.

And what's more, a lot of them appear to have overlapping purposes. The Sovreign and Akira are big fighting ships, the Steamrunner, Intrepid, Norway, New Orleans, Prometheus are all smallish tactical ships and all roughly the same size. Nova and Oberth are both science/scout ships, etc

For that matter, the Nebula's very existence bugs me. It literally has all the exact same parts as the Galaxy, just re-arranged. Why would they even do that? It can't be cost effective and it doesn't hold any aesthetic value. You could literally build a Galaxy class ship for the exact same cost as a Nebula (probably a little less) and not have to devote any extra resources to R&D to reconfigure everything.

Obviously some of this has to do with older ships staying in service for a long time while newer ones are developed, but that doesn't explain away everything. Why would you build Steamrunner/Sabre/Norway classes all at the same time when they are essentially the same kind of ship. Just pick one and build three times as many instead of squandering resources to develop and engineer more and more classes.

Well your guess is as good as mine. I think the real world explanation is likely something along the lines of the ship builders in the FX department being tasked to build multiple ship designs for a particular episode, and those designs not selected get shelved, and then later reused to save costs. In universe explanation is more along the lines that each ship design has a specific role it fills. Since the feds are not on a monetary system, at least one as we know it, it doesn't cost more or less to do this.

As to Nebulas and Galaxies, they were sister designs. The obvious reason is the Nebula is the TNG analogue to the Miranda class, and it was a way to make things interesting for fans.

But you make a good point. Why so many classes, and why do so many seem to hang around, but others get retired? Does this mean some classes are so well designed they stay around for almost a century, while others are considered failures? Or does this mean some ships were pulled out of mothballs to meet the need of a growing Federation, which had a fleet devastated by the Borg and the Dominion war?

For example, if the Miranda class was derived from the Constitution class, and the constitution class was retired after TUC (Caveat: we have to assume this as we never saw Connies in TNG; all we know is the Enterprise A was retired, not necessarily all the Constitutions), then why were the Mirandas still around? Yet both Excelsiors and Mirandas outlasted the Constellation Class and Ambassador class.

Don't get me wrong, that's a good point, but at the same time they aren't building four or five different types of attack subs, nor are there four or five different kinds of capital ships.

I suppose if you assume that most of the ships on the second list were in service as a result of re-arming at wartime, and are now mostly decommissioned, then it makes more sense. But even so, it's still strange because there isn't a lot of diversity among the ship classes. Norway, Steamrunner, Intrepid, Saber all being very similar ships serving similar purposes and all built around roughly the same time.

It's especially odd when you see the same 2-3 ships over and over from the Romulans, Klingons, Cardassians, Dominion, etc.

Starfleet may have many different classes of ship, but they fulfil different roles and duties. Add to that the fact that with many larger/newer classes there won't be many of those ships commissioned straight away, they would take time to build and deploy (I'm sure that there was backstage information that said there were only around 10 Galaxy-Class ships built over the run of TNG; whilst there are at least only two Sovereign-Class ships, the Sovereign and the Enterprise).

As older ships were retired from service newer ones would take their place (Oberth and Nova). We also have no evidence that shows the Prometheus-Class was a success since it was the only named ship of its class (the one seen in "Endgame" could have been the Prometheus, pulled from mothballs to meet the threat entering the Sol System).

^In at least one timeline, the Prometheus-class is still in service in the 26th century (along with the Nova and Nebula classes) in "Azati Prime". They're seen fighting the Sphere Builders.

Unfortuantely, Trek ships vary rarely are shown doing anything aside from the usual stuff. Voyager and the Enterprise-D were identical ability-wise. I doubt there's anything any one of the Excelsior, Miranda, Constitution, Nebula, Constellation, Galaxy, Intrepid, NX, Sovereign and Akira classes can do that the others couldn't. They're a bunch of different shapes but the same stuff inside.

Because the advent of CGI made it cheaper to build models and give the producers something "new" all the time. In-universe, clearly significant advances were made in the areas of industrial replication and computer simulation, allowing Starfleet designers and engineers to revise components and experiment with hitherto unseen architecture.

Shipyards closer to Earth were equipped with the new technology sooner than those in the vicinity of DS9, which had to make do with reused components (read: motion control still being used in parallel with CGI). However, by the late 2370s, the new technology became nearly ubiquitous, which makes future component reuse fairly unlikely save in the hands of certain fan-modellers.

If we try to equate Star Fleet and it's ship classes to real life fleets, perhaps the number of ship classes seems high.

If we consider that Star Fleet gets ships from the combined output of over 100 worlds in the galaxy (well beyond our experience) perhaps there should be hundreds of ship classes and thousands of vessels.

But that's not what we see onscreen, only in way-off-canon novels or fanfic. There is no reason to suspect that the shows were heavily biased towards a certain fraction of Starfleet. A number of episodes showed us locations far from the main series settings (the UP shipyards, for example), and the producers didn't request new ship designs for those stories – what would be the point? The LightWave fleet represented the 2370s, the miniature/kitbash fleet the 2360s and the 2280s, and so forth.

For that matter, the Nebula's very existence bugs me. It literally has all the exact same parts as the Galaxy, just re-arranged. Why would they even do that? It can't be cost effective and it doesn't hold any aesthetic value. You could literally build a Galaxy class ship for the exact same cost as a Nebula (probably a little less) and not have to devote any extra resources to R&D to reconfigure everything.

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You're making rather a large assumption there. Yes, the primary hull and the warp nacelles appear to be identical, but can we say the same for the interior components? Is the warp core as efficient? Are the sensors as effective? Are the engines as powerful?

It may be that the Nebula class fits tried and tested equipment within it's hull, whilst the Galaxy is, for it's time, cutting edge. After all, the Galaxy is designed for long range missions into unexplored territory, possibly away from Federation space for years at a time. It has to be entirely self sufficient. The Nebula does not appear to have been used for such long term missions. A ship that can regularly visit a Starbase for routine maintenance and resupply needn't be built to the same exacting standards as one that has to look out for itself.

I can also imagine that construction of the Galaxy class hull would require specialist facilities. If so, then it would actually be economical to use those facilities to construct parts for Nebula class ships. Better than letting them sit idle once the limited run of Galaxys was done.

5 different active service attack sub classes were built in Germany, 6 in Russia.

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It occurs to me that all the Nebula class ships might be precursors of the Galaxy class, the Galaxys are a follow on class, with the Nebula construction being discontinued prior to the construct of the first Galaxy.

Just looking at a list of active ships in any major navy right before World War 2 should prove the point that any "fleet" would become quite diverse in short order.

Older types remaining in service from earlier eras, newer types recently added to a fleet and brand-new models just coming into service; would all end up serving side-by-side.

In the US Navy (again, American bias!) prior to and during World War 1 - there were about 12 classes of Destroyers (alone) built and many were still in service in 1918.

Some of those WW1 Destroyers were still in service during WW2 - in addition to 13 newer classes built between the wars and during WW2. Again, just Destroyers... If you start looking at Battleships, Cruisers, Carriers, Submarines etc. - the list just keeps growing.

It occurs to me that all the Nebula class ships might be precursors of the Galaxy class, the Galaxys are a follow on class, with the Nebula construction being discontinued prior to the construct of the first Galaxy.

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(Yes, I had to quote the ginormous smilie.)

I like it. This is probably close to true - I mean, apparently the Galaxys were in development hell for a while, so maybe the Nebulas were meant to prove the concept and technology behind them, as well as fill in a support role once the Galaxys came online. Thus, they'd already all be built and in service by early in the Galaxy production run if not before.

5 different active service attack sub classes were built in Germany, 6 in Russia.

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It occurs to me that all the Nebula class ships might be precursors of the Galaxy class, the Galaxys are a follow on class, with the Nebula construction being discontinued prior to the construct of the first Galaxy.

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The Brits might get mad at having one of their classes included with the Americans (Trafalgar).

What was worse though in the Cold War, when pretty much the Cruisers, the destroyers, and the Frigates were all doing the same thing (Anti-Submarine Duties), except for a few large WWII cruisers that were converted to flagships. Even the Soviets decided to build the largest warship (outside carriers) devoted to ASW (Kirov's).

In re Starfleet, we just haven't seen them do too much on-screen other than failed explorers, guest star character transports, and cannon fodder in terms of non-hero ships.

5 different active service attack sub classes were built in Germany, 6 in Russia.

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It occurs to me that all the Nebula class ships might be precursors of the Galaxy class, the Galaxys are a follow on class, with the Nebula construction being discontinued prior to the construct of the first Galaxy.